Drilling mud is known to represent a heterogeneous system which inevitably contains colloidal solid phase particles. The presence of such particles in drilling mud determines a number of important geological properties of drilling mud from the viewpoint of well drilling performance. Drilling mud is required to retain these properties to ensure best drilling performance. However, a steady maintenance of these properties during drilling is a very difficult problem.
The vast majority of drilling operations are conducted in clayey rocks. Clayey rocks being drilled are partly dispersed and get to the drilling mud in the form of colloidal particles to cause a substantial change in the composition of drilling mud even after several pumping cycles.
Various methods for separating solid phase from drilling mud should be used for the restoration of its properties. Therefore, economical and efficient separation of solid phase from drilling mud or, which is the same, an efficient cleaning of drilling mud from drillings (solids) has a decisive importance in the well drilling process.
Technical and economical performance of drilling depends to a large extent on quality of drilling mud used and the degree of its cleaning from drillings.
High-grade cleaning of drilling mud improves mechanical speed of drilling and conditions for operation of drill bits and equipment. In addition to an improvement of mechanical speed of drilling, high-grade cleaning of drilling mud contributes to reduced consumption of materials used for maintaining properties of drilling mud, prolongs the life of drilling mud and reduces complications and emergency situations during drilling.
Low quality of drilling mud cleaning is the main cause of emergency situations and complications associated with mud absorption, jamming of drilling and case pipes, avalanches from well walls.
Therefore, high-grade cleaning of drilling mud from drillings is the most important technical step during drilling which substantially affects technical and economical performance of well drilling.
All existing methods for cleaning drilling mud enable the removal of only some part of solid phase from the drilling mud at different rate and quality. All these methods have, however, a number of disadvantages inherent in the very concept of separation on which they are based. Thus, minimum size of particles that may be separated from drilling mud on vibratory screens depends on the mesh size of a screen. With a reduction of mesh size to improve quality of cleaning, the throughput capacity materially decreases and drilling mud losses with solids increase.
In cleaning with the employment of hydrocyclones, coarse and heavy-weight particles of solid phase are removed from drilling mud. Finer and light-weight particles (below 20 .mu.m) cannot be removed in hydrocyclones and other cleaning apparatus.
Known in the art is a method for, regenerating drilling mud, wherein drilling mud leaving the well and containing drillings is preliminarily diluted and separated from coarse particles of drillings. Fine non-charged particles of drillings remain in such diluted and cleaned drilling mud, as well as negatively charged colloidal clayey particles. Subsequently negatively charged clayey particles are separated from the drilling mud by depositing them to a rotary anode with subsequent removal by means of a scaper. The deposited negatively charged clayey particles entrain a part of non-charged particles which are also deposited on the rotary anode (cf. Czechoslovakian Pat. No. 109992, cl. 5a, 31/20, issued on Feb. 12, 1964).
Using the above-described method, only a part of drilling mud can be cleaned, and the remaining part of drilling mud is fed to the well without cleaning.
Cleaning only a part of drilling mud and the separation, of coarse particles first, and then fine particles is very complicated under production conditions, hence, costly.